Joseph Gordon-Levitt was at the Coolidge Corner Theatre on Tuesday night to screen his directorial feature debut, “Don Jon,” about a man with a pornography addiction who attempts a healthy relationship. Gordon-Levitt, who starred in “Looper” and “(500) Days of Summer,” sat in the Brookline audience with friends for the entire movie, and then hopped onstage to answer questions about the project and his costars, who include Scarlett Johansson, Julianne Moore, and Tony Danza. Gordon-Levitt told the group that he wrote Johansson’s part with her in mind (luckily, she said yes to the role), and that Danza — who plays his father — also starred with him in the 1994 movie “Angels in the Outfield.” Oddly enough, that film also helped launch the careers of Adrien Brody, Matthew McConaughey, and Boston-bred Neal McDonough, who portrayed baseball players.